Method of and apparatus for sink and float separation of fine coal and the like



Aug. 28, 1956 N. L. DAVIS METHOD OF AND APPARATUS FOR SINK AND FLOAT SEPARATION OF FINE COAL AND THE LIKE 4 Sheets-Sheet 1 Filed May 6, 1952 I72 06% for JVeZaon iiflaz/zls Aug. 28, 1956 N. L. DAVIS 2,760,633

METHOD OF AND APPARATUS FOR SINK AND FLOAT SEPARATION OF FINE COAL AND THE LIKE Filed May 6, 1952 4 Sheets-Sheet 2 I 7 yeifior Jis we .Z..Da 0zl5 fwqaw/ g- 1956 N. DAVIS METHOD OF AND APPARATUS FOR SINK AND FLOAT SEPARATION OF FINE COAL AND THE LIKE I 4 Sheets-Sheet 3 Filed May 6, 1952 l J t 1: 5 I I I72 van for J Zsan llflavz's Aug. 28, 1956 N. L. DAVIS 2,750,633

METHOD OF AND APPARATUS FOR SINK AND FLOAT SEPARATION OF FINE COAL AND THE LIKE Filed May 6, 1952 4 Sheets-Sheet 4 .llllm" I7? 067? for J eZs 02217. Daa'zls yW M United States Patent METHOD OF AND APPARATUS: FOR SINK AND SEPARATION OF FIN-E COAL AND THE Nelson L. Davis, Chicago, Ill.

Application May 6, 1952, Serial No. 286,250

Claims. (Cl. 209-1725) My invention relates to. improvements in method and apparatus for sink and float separation of fine coal and the like.-

My invention is especially applicable to a system wherein a bath of sink and float medium or parting liquid is maintained at a specific gravity greater than that of some and less than that of other of the elements to be separated and wherein the medium comprises finely divided magnetically susceptible solids or media such: as magnetite and the like in suspension in water. For convenience, I refer hereafter to the parting liquid as the medium and to the magnetically susceptible solids as magnetic media or media.

The specific gravity of the medium depends on the concentration of media therein. The media tend to sink in the bath under the influence of gravity. It is essential that the specific gravity of the bath be uniform from topto bottom. Such uniformity results from the upward movement of the medium at a rate approximating or preferably slightly higher than, the sink rate of the media, the medium circulating through the bath from supply atthe bottom to withdrawal from the top. The rate of upward movement must always be so low as to avoid any appreciable effect on the material being separated, so that pure sink and float separation may take place without any appreciable upward current classification.

The material to be separated is fed to the bath, the heavy solids report to the bottom, the light solids float to the top and the separated sink and float solids are separately discharged from the bath with a substantial amount of medium.

While my invention is applicable to the treatment of all sizes and types of coal, ore and the like wherein it is desired to separate elements of varying specific gravity, the present application is especially well adapted to the treatment of very fine coal, such as feed solids of minus one-quarter A) inch.

The problem of gaining an accurate sink and float separation in connection with such. size solids, especially coal, lies in the fact that small size sink has only slightly greater settling velocity than the magnetite used as media. Therefore it is mandatory that some means be devised which will permit sharply accurate control of bottom inlet medium in volumetric quantity which will result in rising current velocities barely suflicient to maintain the magnetite in hydraulic suspension but yet which will be low enough to permit the sink solids to descend counted to the rising current needed to support the media. For example, if it is found that magnetite has a settling velocity in water of sixty feet an hour, upwardly rising currents of sixty feet an hour are needed to support the magnetite in a state of hydraulic suspension. If sink solids out of the feed are found to settle in water at velocities greater than sixty feet per hour, then a float and sink separation is possible but if such settling velocities are not greater than the magnetite, a float and sink separation is impossible.

It is a well known fact that a particle of a given size 2,760,633 Patented Aug. 28, 1956 ine and of a density less, by a given amount than the density of the parting liquid will have the same rising velocity in the parting liquid as the settling velocity of a particle of the same size and having a density of the same given amount greater than the density of the parting liquid.

In the case stated above it will furthermore be noted that where the separation of float and sink solids commences at or near the surface of the bath the; sink solids must descend counter to the rising current needed to support the media. With a submerged type feed of vessel the sink solids are forcefully submerged alongwith the float solids which are then subsequently released to rise in the bath. An important advantage gained is. that. here the rising currents needed to support the, media assist rather than retard the upward movement of the float.

An inlet slotted manifold in combination with a feed inlet control valve and an outlet control valve will sup. ply the precise margin of control essential to the success of this endeavor.

It should be noted that the downwardly directed. flow of inlet media should not penetrate deeply enoughinto the compartment of the rotor to agitate and resuspend near gravity small size sink solids. However, some agitation is necessary and some means must be provided to dispose of misplaced float material entrained with the sink in the bottom zone of the vessel bath. Toward this end we show arcuate inclined rotor vanes or flights. These are streamlined in much the same manner as the vanes of a steam turbine rotor. The result is as the rotor revolves through the liquid medium any solids in suspension are caused to flow in an inward direction and away from the hydraulic. drag influence of the moving rotor. To better explain this point visualize flights mounted radially. If such were done, the tendency would be for the rotor to move the liquid bodily forward in the direction the rotor is traveling. There would be no tendency other than from the vertical force of buoyancy for any float solids to leave the liquid being propelled forward by the rotor. With the streamlined flight shown, the inward movement of such, float particles is. assisted. In shutting down to cease operation of the device, the rotor and medium recirculating pump continue to operate for a few minutes after feed of raw material is cut off from the vessel.

After two or three minutes time have elapsed, sulficient for nearly all of the float and sink solids to have been evacuated, the drain plug shown in the bottom center of the vessel is opened, allowing the bowl of the vessel to be drained. Solids would have to travel counter to gravity to enter the medium inlet manifold during this operation and of course they will not. When the facilities are again placed in operation and the vessel is again filled with medium the inlet manifold, having a slotted discharge orifice, has very little tendency to become plugged and it would indeed take an unusually large amount of coarse size solids to seriously impede its eflicient operation.

Another point of great importance is found in th IQiOr channel on the reject side. Here the flights of the rotor revolve in an upward direction. Note that the perforations of the flight are principally located in the outer portion of the area of the flight, in other words, the section furthest removed from the center ofthe rotor. The curved shape of the flight permits this outer section to emerge above the liquid level in the contained rotor channel, leaving medium free to drain through the perforated holes in an unobstructed manner because the slope of the flight is sufficiently great to permit sink material to slide downward and occupy the innermost area of the flight surface. Nevertheless, a slight pumping head is developed in this section of the rotor channel and the liquid level will be a few inches higher than the bath level in the main zone of the vessel. This results in an hydraulic current which is released in the zone immediately below the lower extremity of the inner trough plate of the rotor channel. As the following flight approaches the point where it will seal the escape of liquid, the velocity of the inwardly flowing current is increased and in this manner any semi-buoyant float solids will be forced inwardly to the zone of the bath where they will have plenty of time to rise and properly join the remainder of the float product of the separation. Without this feature there would be a marked tendency for such semi-buoyant float to be improperly discharged with the sink product.

Another important point is that the new design lends itself well to the important advantage of adaptability to handle high unit capacity rates. All we need to do is increase the width of the vessel while its diameter remains the same. In other words, the width of the vessel at ten feet is usually great enough to handle a feed rate of one hundred tons per hour of one-quarter inch by one-half millimeter 4 x /2 mm.) feed coal. There would be no mechanical or functional difliculty experienced in doubling the Width of the rotor to twenty feet and doubling the feed capacity to two hundred tons per hour and it would still be a single unit instead of two separate units as heretofore has been necessary. This is made possible by the unique mechanical and structural method of introducing bottom inlet medium under absolute control.

In the above, I have referred to settling velocity rates for both media and sink solids. Nothing has been said about rising velocity of float solids which would apply in case all of the feed material was forcefully submerged to the lower zone of the bath from which point the buoyancy of the float would cause it to rise and be separated from the sink material which would remain in the bottom zone.

My invention is illustrated more or less diagrammatically in the accompanying drawings, wherein:

Figure l is a side elevation of my processor;

Figure 2 is an end elevation;

Figure 3 is a section along the line 33 of Figure 2;

Figure 4 is a section along the line 44 of Figure 3;

Figure 5 is a section on an enlarged scale through one of the rotor flights;

Figure 6 is a section on an enlarged scale along the line 66 of Figure 4 showing a detail;

Figure 7 is a plan view on an enlarged scale of the vessel drainage valve shown in section in Figure 3.

Like parts are indicated by like characters throughout the specification and drawings.

1 is a generally cylindrical vessel open at the top, supported on legs 2, projecting respectively from the fluid discharge end 3 of the vessel and from the fluid entrance end 4 of the vessel 1. 5 is a rotor contained within the vessel 1. The rotor includes two or more annular rings 6, 7, 8 tied together by through bolts 9 and nuts 10, the bolts extending outwardly at each end of the vessel through a rotor track ring 11. Mounted within the vessel is a fixed track ring 12. Rollers 13 are interposed between the two track rings, being held in position in annular arrangement by parallel spaced roller rings 14. 15 indicates the rotor drive shaft, a driving connection between it and the roller taking the form of any suitable annular rack and gear arrangement. The details forming no part of my invention are not further illustrated. The drive shaft 15 carries a sprocket 16 driven by chain 17 from sprocket 18 in turn driven by a motor 19 so as to rotate the rotor in a clockwise direction as shown by the arrows in Figures 2 and 4.

Held between the plates 6, '7, 8 are a plurality of flight frames 20, supported at 21 on through bolts 9 extending the length of the rotor through the rings 6. These frames terminate at their outer ends in shoes 21, 22 adapted to just clear the inner periphery of the wall of the vessel 1.

The frames are tied together by bolts 23 and each frame carries a curved flight blade 24 socketed therein. The flight blades are apertured as at 25, there being more apertures toward the outer end of the blade. The surfaces of the shoes 21 and 22 in alignment with the blades 24 form a curved plow-like element or flight. These flights are outwardly and forwardly extended along curved lines as indicated especially in Figure 4.

26 is a raw material feed chute mounted above the open mouth of the vessel and extending the full width of the rotor.

Located within the vessel mounted on the ends 3 and 4 is a segmental curved inner feed trough plate 27, extending from above the feed chute to well below the level of the liquid in the vessel so that raw material fed to the vessel through the chute 26 is deposited in the pockets between successive flights and is carried downwardly along the cylindrical passage between the outer periphery of the vessel and the inner trough plate 27, below the surface of the liquid. In order that there be no crushing of material as the successive flights pass out of register with the chute, the lower portion of the chute is formed of a wall 28 pivoted at 29 and provided with a counter-balance 30 so that if a piece of coal or ore is caught between the flight and the wall, the wall may yield in order to permit the object to drop into the pocket.

31 is a curved inner sink discharge trough plate concentric with the plate 27 equally spaced from the inner periphery of the vessel and extending from below the level of liquid in the vessel to its termination in a refuse or sink chute 32 above the liquid level.

Raw material entering the vessel through the chute 26 is forcibly carried downwardly in successive batches to a point below the surface of the medium, where the float being of lower specific gravity than the medium may escape to rise to the surface and the sink of higher specific gravity will be picked up by the flights, carried above the level of the medium along the plate 31 and discharged into the chute 32. 33 indicates a weir in two parts separated by the chute 32 over which medium and. float solids may flow. The details of the means for handling both sink and float solids after they leave the vessel form no part of the present invention and are not here illustrated.

Medium, that is the parting liquid, is supplied to the vessel through the duct 34 by any suitable pump means. As a general proposition, medium escaping from the vessel with the discharge of finished product will be recirculated for return to the vesel through the pipe 34. The details of this arrangement form no part of the present invention. The pipe 34 has branches 35, 36 controlled by valves 37, 38 to supply controlled volumes of medium to the medium supply nozzles 39, 40 in the fluid supply end of the vessel so as to set up a current of medium across the upper surface of the medium toward the discharge weir.

The pipe 34 has an extension 41 beyond the branches 35 and 36 which, controlled by a valve 42, discharges medium through the pipe 45 to the distribution box 46 at the upper end of the sink chute, the box having a roof 47 to constrain the flow of medium to a thin sheet along the floor of the refuse chute 32 so as to insure that any sink material deposited in the chute will be washed out of the vessel.

Extending at right angles to the pipe 34 is a pipe 48 controlled by the valve 49 and discharging into the inlet medium manifold 50. This manifold decreases in cross sectional area from the entrance to the exit at 51, controlled by a valve 52. The manifold is closed at top and sides and has a discharge port 53 extending the entire length of the vessel. The tapered cross section of the manifold insures that no matter what the medium pressure in the manifold may be and no matter what the volume of medium discharged may be, the discharge will 5 be the same at any point from end to end of the manifold.

54 is a valve housing on the underside of the vessel. It discharges through a pipe 55 to any suitable reservoir or sump. 56 is a disc valve in the valve housing movable to open or closed position to control the drainage port 57. As shown, the valve is actuated by a piston 58 carried by a piston rod 59, the piston reciprocating in a cylinder 60, controlled by the fluid lines 61 from any suitable control mechanism. The valve 56 is centered in the valve housing 54, held against rotation by the key 62 and is provided with arms 63 projecting laterally beyond the valve seat 64 so that when the valve is unseated by moving downwardly in the valve housing 54 there is ample clearance for passage of medium downwardly from the vessel through the discharge pipe 55.

I have shown the sink chute discharging from the same end of the vessel as the discharge of the float over the weir. Under some circumstances, it is desirable to discharge the sink from the opposite end of the vessel. This can be accomplished with a slight rearrangement of the duct 34 and the associated pipes and valves, in which case, the sink chute would be downwardly inclined in the opposite direction.

65 is a baflie plate extending from end to end of the vessel on the refuse side. It extends from approximately the level of the weir 33 downwardly to a point below the lower extension of the sink discharge trough plate 31, being spaced inwardly therefrom. As the flights move upwardly along 31, they effect a pumping action and raise some of the medium above the level of the medium in the remainder of the vessel. That medium flows downwardly below the plate 31 and is discharge by the pressure head resulting into the main body of the vessel, setting up a cross current which is interrupted by the baflie 65. This cross current is the result of this downward flow and pressure head and also the result of the streamlined contour of the flights so that any teeter material still in suspension in the liquid in front of the flight not yet settled on the flight will flow centripetally toward the vessel and when interrupted by the bafl le 65, such flow will tend to urge the sluggish float particles upwardly for discharge over the weir 33. A substantial amount of sluggish float material which had not yet made up its mind where to go but which really belongs with the float, is thus kept from discharging with the sink.

The downward discharge of medium through the discharge port 53 is not SllfllCl611t to cause any appreciable agitation in the zone between the port 53 and the outer periphery of the vessel. Some such agitation is essential to insure freeing of any entrapped float solids from the sink at the bottom of the vessel. This agitation is accomplished by the shape and movement of the flights and any entrapped solids which are free are urged inwardly centripetally by the passage of the flights.

By this arrangement, I am enabled to provide sufficient upward flow of the medium to maintain the media in hydraulic suspension and I am enabled to provide between the point at which the medium is introduced to the vessel adjacent the bottom, an agitation and a centripetal flow of liquid of low magnitude but of sufficient magnitude to rescue entrapped float from the sink.

I claim:

1. In combination, a generally cylindrical vessel, adapted to contain a quiescent heavy medium sink and float solids separation bath, a rotor rotatable therein about a horizontal axis, having outwardly and forwardly inclined arcuate flights adapted to travel along the bottom of the vessel, each flight being adapted when traveling to impel a separate gentle current in the bath up wardly and inwardly from the bottom thereof, a sink discharge trough plate concentric with the vessel having its lower extremity below the level of the bath and defining with the vessel wall a channel through which successive rotor flights pass upwardly developing a slight 6 pumping head above the level of the bathliquid, a baffle wallin front of the trough plate extending downwardly below the extremity of the rotor channel and upwardly toward the surface of the bath.

2. In combination, a generally cylindrical vessel, adapted to contain a quiescent heavy medium sink and float solids separation bath, a rotor rotatable therein about a horizontal axis, having outwardly and forwardly inclined arcuate flights adapted to travel along the bottom of the vessel, each flight being adapted when traveling to impel a separate gentle current in the bath upwardly and inwardly from the bottom thereof, a sink discharge trough plate concentric with the vessel having its lower extremity below the level of the bathand defining with the vessel wall a channel through which successive rotor flights pass upwardly developing a slight pumping head above the level of the bath liquid, abaffle wall in front of the trough plate extending downwardly below the extremity of the rotor channel and upwardly toward the surface of the bath, the flights being perforate toward their outer extremities to permit the escape of some of the fluid in front of each flight as the flight rises above the surface of the bath.

3. In combination, a generally cylindrical vessel, adapted to contain a heavy medium bath, a rotor rotatable therein about a horizontal axis, having outwardly and forwardly inclined arcuate flights adapted to travel along the bottom of the vessel, each flight being adapted when traveling to impel a separate gentle current in the bath upwardly and inwardly from the bottom thereof, means adjacent the bottom of the vessel but above the rotor for supplying medium to the vessel and: for directing the medium for downward flow' toward the rotor.

4. In combination, a generally cylindrical vessel, adapted to contain a heavy medium bath, a rotor rotatable therein about a horizontal axis, having outwardly and forwardly inclined arcuate flights adapted to travel along the bottom of the vessel, each flight being adapted when traveling to impel a separate gentle current in the bath upwardly and inwardly from the bottom thereof, a sink discharge trough plate concentric with the vessel having its lower extremity below the level of the bath and defining with the vessel wall a channel through which successive rotor flights pass upwardly developing a slight pumping head above the level of the bath liquid, a baffle wall in front of the trough plate extending downwardly below the extremity of the rotor channel and up wardly toward the surface of the bath, means adjacent the bottom of the vessel but above the rotor for supplying medium to the vessel and for directing the medium for downward flow toward the rotor.

5. In combination, a generally cylindrical vessel, adapted to contain a heavy medium bath, a rotor rotatable therein about a horizontal axis, having outwardly and forwardly inclined arcuate flights adapted to travel along the bottom of the vessel, each flight being adapted when traveling to impel a separate gentle current in the bath upwardly and inwardly from the bottom thereof, means adjacent the bottom of the vessel but above the rotor for supplying medium to the vessel and for directing the medium for downward flow toward the rotor, the medium supply means including a manifold extending across the bath having a discharge port along the underside thereof, a drainage aperture in the bottom of the vessel in opposition to the medium supply.

6. In combination, a generally cylindrical vessel, adapted to contain a heavy medium bath, a rotor rotatable therein about a horizontal axis, having outwardly and forwardly inclined arcuate flights adapted to travel along the bottom of the vessel, each flight being adapted when traveling to impel a separate gentle current in the bath upwardly and inwardly from the bottom thereof, a sink discharge trough plate concentric with the vessel having its lower extremity below the level of the bath and defining with the vessel wall a channel through which successive rotor flights pass upwardly developing a slight pumping head above the level of the bath liquid, a baflle wall in front of the trough plate extending downwardly below the extremity of the rotor channel and upwardly toward the surface of the bath, means adjacent the bottom of the vessel but above the rotor for supplying medium to the vessel and for directing the medium for downward flow toward the rotor, the medium supply means including a manifold extending across the bath having a discharge port along the underside thereof, a drainage aperture in the bottom of the vessel in opposition to the medium supply.

7. In a cylindrical sink and float separating vessel, a plurality of spaced longitudinally disposed conveyor flights in working relationship with the inner periphery of the vessel and mounted for rotation about the horizontal axis thereof, means for supplying a parting liquid to the vessel for downward flow into the path thereof immediately above the path of the innermost boundaries of the flights at the bottom of the vessel, the medium supply means including a manifold extending substantially the entire length of the flights, having a downwardly open port for substantially its entire length and means for supplying medium to such port for discharge therethrough at uniform velocity and volume from end to end, means for discharging medium from the vessel adjacent the upper portion thereof.

8. In a cylindrical sink and float separating vessel, a plurality of spaced longitudinally disposed conveyor flights in working relationship with the inner periphery of the for discharging medium from the vessel adjacent the upper portion thereof, a discharge port in the bottom of the vessel and a valve for opening and closing it to drain the vessel.

9. In combination, a vessel adapted to contain a heavy medium bath, solids conveying means mounted for generally horizontal movement adjacent and above the bottom of the vessel, means adjacent the bottom of the vessel above the solids conveying means for discharging a relatively restricted stream of heavy medium for downward flow toward the bottom of the vessel and across the path of the solids conveying means, means for discharging medium from the bath adjacent the surface thereof.

10. In combination, a vessel adapted to contain a heavy medium bath, solids conveying means mounted for generally horizontal movement adjacent and above the bottom of the vessel, means adjacent the bottom of the vessel above the solids conveying means for discharging a relatively restricted stream of heavy medium for downward flow toward the bottom of the vessel and across the path of the solids conveying means, means for discharging medium from the bath adjacent the surface thereof, the cross sectional area of that part of the bath through which the medium travels upwardly toward the discharge means being substantially greater than the cross sectional area of the downward flowing medium stream where it crosses the path of the conveying means.

References Cited in the file of this patent UNITED STATES PATENTS Re. 16,674 Chance July 12, 1927 170,312 Stanberrie Nov. 23, 1875 815,093 Keeney Mar. 13, 1906 1,710,568 Carl et a1. Apr. 23, 1929 2,203,601 Rakowslty June 4, 1940 2,263,168 Dorr et a1 Nov. 18, 1941 2,440,097 Kear Apr. 20, 1948 2,479,141 Smith Aug. 16, 1949 2,516,962 Davis Aug. 1, 1950 

6. IN COMBINATION, A GENERALLY CYLINDRICAL VESSEL, ADAPTED TO CONTAIN A HEAVY MEDIUM BATH, A ROTOR ROTATABLE THEREIN ABOUT A HORIZONTAL AXIS, HAVING OUTWARDLY AND FORWARDLY INCLINDED ARCUATE FLIGHTS ADAPTED TO TRAVEL ALONG THE BOTTOM OF THE VESSEL, EACH FLIGHT BEING ADAPTED WHEN TRAVELING TO IMPEL A SEPARATE GENTLE CURRENT IN THE BATH UPWARDLY AND INWARDLY FROM THE BOTTOM THEREOF, A SINK DISCHARGE TROUGH PLATE CONCENTRIC WITH THE VESSEL HAVING ITS LOWER EXTREMITY BELOW THE LEVEL OF THE BATH AND DEFINING WITH THE VESSEL WALL A CHANNEL THROUGH WHICH SUCCESSIVE ROTOR FLIGHTS PASS UPWARDLY DEVELOPING A SLIGHT PUMPING HEAD ABOVE THE LEVEL OF THE BATH LIQUID, A BAFFLE WALL IN FRONT OF THE TROUGH PLATE EXTENDING DOWNWARDLY BELOW THE EXTREMITY OF THE ROTOR CHANNEL AND UPWARDLY TOWARD THE SURFACE OF THE BATH, MEANS ADJACENT THE BOTTOM OF THE VESSEL BUT ABOVE THE ROTOR FOR SUPPLYING MEDIUM TO THE VESSEL AND FOR DIRECTING THE MEDIUM FOR DOWNWARD FLOW TOWARD THE ROTOR, THE MEDIUM SUPPLY MEANS INCLUDING A MANIFOLD EXTENDING ACROSS THE BATH HAVING A DISCHARGE PORT ALONG THE UNDERSIDE THEREOF, A DRAINAGE APERTURE IN THE BOTTOM OF THE VESSEL IN OPPOSITION TO THE MEDIUM SUPPLY. 